I Have a1991 CHevy W/T 2wd that has a blown 4.3L v6 in it currently. I have been told that all is needed to swap a 350 in are new TB injecters and brain box. Will the Engine mounts match up with a 350? and will the radiator be able to support a 350 or will that need to be changed? Any ways the truck is in very good shape and has true duel exhaust on it which brings up another question? Will shorty headers on a 350 or the stock exhaust manifold match up with the exhaust tubing that was built for the 4.3L? Any advice or answers would be appreciated.

 

I think you would need to swap to a 5.3 not 5.7 to get the mounts to match. not sure on the headers but I dont think they would without a little work nothing a good muffler shop couldnt handle. How big is the radiator? youj might want to go with electric fans. If you are looking for performance you should go with the 6.0 or 6.2.

 

Best bang for the buck:
Go to the bone yard and get a vortec 350 newer truck. Pull all the wiring out, all engine components, engine and the brain. The block should match the 4.3 mounts. Original radiator will work, getting a bigger one will only help things. Fuel system should work with the correct regulator (buy an adjustable one). Mount Vortec brain box in another location (not the stock poistion for the 91) I dont think it will fit behind the glovebox. Maybe the firewall? You might have to have the PCM reflashed for the 700R4 transmission but it will bolt right up to the 350.

OR

Next best thing on performance but easier to pull it off:
Get a TBI 350 and swap out the heads with vortec centerbolt heads. Then swap the injectors on the 4.3 TBI with bigger ones. You could also get an edlebrock TBI unit for some more performance. 454 SS TBI will work too. Or you can simply leave it stock. Then go to TBIchips.com and ask him for a PROM for a 4.3 to 5.7 swap. He will hook you up for around $35. You can use the stock 4.3 brain box and simply plug the modified PROM in. Once again trans will bolt right up and the stock fuel pump from the 4.3 will work. The stock regulator on the 350 will work too.

Not 100% on headers. I had Summit brand shorties that bolted up to my Y pipe on my 91' GMC with a 5.0. I don't see the 4.3 being that different but Im not sure.

While you have it out you could get a better cam and using an aftermarket intake that has the same
size runners and flow as the vortec heads will help too.

 

Ya im not going for all out performance...atleast not yet right now i want to get it up and running again. I have been also considering putting another 4.3 in it and then later dropping a supercharger on it but not sure. Im moving to Texes so i also need to find out where they stand on replacing the stock motor with a bigger one. I know some places they will give you a hard time and not pass if for IM.

 

I watched them do this swap on TV one day. They made it look really simple (of course they did, it's tv). Everything bolted up, they swaped the injectors for V8 ones and reflashed the computer, that was it.They keptthe radiator. Nowadayswiththe out of controll gas prices, i would consider keeping the 4.3. They are great motors and are very easy to find, every astro van had one. Man i wish i had a 4.3 this 6.0 is killing me.

 

Your best be would be a 350 slightly modded. What you should do is make the effort to put Vortec heads on a TBI 350. Then simply have someone make a new PROM for your ECU and throw on a 14" open air cleaner with a K&N and you will get better gas mileage than a 4.3 and still have more power on tap. The money you'll save on gas will pay for the heads in one years time. A 2mpg gain over the course on the year will save you roughly $500 a year or more. Its easy, fairly inexpensive and you'll be happy with the results. You can get a TBS for $25 for a TBI motor and get roughly 1 more mpg. Get a torque curve TBS tho, it helps more a crusing speeds.

I did this exact thing to my 5.0 in my 91'. I had TBIchips make me a stage 1 PROM after I put on the heads, threw on a 14" K&N open air filter and a TBS and it had more *****. The city mileage was the same but I gained 2-3 mpg on the highway easy.